* Victim Kamene Okonjo, 82, is wife of traditional ruler
* Daughter Ngozi Okonjo-Iweala seen as key reformer
* Police receive phone call making demands (Adds phone call from suspected abductors)
By Tim Cocks and Anamesere Igboeroteonwu
ABUJA/ONITSHA, Dec 10 (Reuters) - Nigerian police were searching for the 82-year-old mother of the country's finance minister on Monday after she was kidnapped from her home by unknown assailants.
Authorities said Kamene Okonjo was seized in Delta state in the southeast late on Sunday morning. They said a rescue operation was under way.
"The kidnappers have made their first call, making some demands but we have to identify the source of the call," said police spokesman for Delta state Sergie Ezegam.
"We still don't know the reason for her abduction."
"What we know is that this is a crime, the woman's life is in danger and we are making frantic efforts to rescue her."
Okonjo is a professor and the wife of the traditional ruler of her home town Ogwashi-Uku.
President Goodluck Jonathan appointed Okonjo's daughter as finance minister last year. Ngozi Okonjo-Iweala's drive to reform a corrupt and closed economy has made her popular with Western powers and many Nigerians hoping for change.
But the former World Bank director has also ruffled powerful vested interests along the way, especially fuel marketers benefiting from a corrupt state subsidy scheme.
Speaking on local independent TV station Channels TV, Delta state Governor Emmanuel Uduaghan said a rescue operation was under way.
"I have directed that within 24 hours the woman should be fished out," he said.
An official in Delta State said investigations had not yet revealed whether she was kidnapped to extract a ransom or for political motives, but that Okonjo was involved in local politics and that seizing her may be some kind of scare tactic.
"If they are pledging to rescue her within such a short timeframe, that probably means they know something about where she is and how to find her," the official said.
Nigeria is one of the worst countries in the world for kidnapping, a business which makes millions of dollars a year for criminal gangs.
Abductions are most common in oil-producing areas like Delta state, where gangs are usually after ransom. The majority of people abducted are Nigerians, but foreign oil and construction workers have also been targets.
Local newspapers report kidnappings almost daily and the victims are often professionals or relatives of politicians, although rarely anyone as prominent as Okonjo. (Editing by Andrew Roche)